A conventional variable-capacity air conditioner changes a flow amount of refrigerant by changing a rotation speed of a compressor with an inverter. In order to obtain an optimal flow amount of refrigerant, Japanese Patent Laid-Open Publication No.06-281296 and Japanese Patent Laid-Open Publication No.2002-89976 disclose a mechanically-controlled expansion valve and an electronically-controlled expansion valve which function as throttle valves for controlling the amount of the refrigerant flowing through a refrigerant passage according to a pressure or temperature in a refrigeration cycle, respectively.
The mechanically controlled expansion valve incidentally controls the flow amount of the refrigerant by detecting the pressure or temperature in the refrigeration cycle. When a load to an electric motor driving a compressor drastically and rapidly increases upon the compressor starting up, a discharge pressure of the compressor drastically increases due to a delay of a driving operation, accordingly providing the motor with an overload. The overload may force stopping the motor (breakdown) or activates an overload relay to stop the compressor.
The electronically controlled expansion valve which can avoid the overload described above, however, has a complicated structure and an expensive production cost.